CHINOOK STORY , Closer To The Truth ..by Robin Clark

THE CHINOOK ZD576 STORY - Closer To The Truth - by Robin Clark - Examining the Facts

THE PROLOGUE

In this tragic aircraft crash , the most intriguing fact is that they were flying toward a most unlikely waypoint , way up on a mountainside . This was found programmed into the main navigation computer by accident investigators..........

There are several ways the co-ordinates , mainly the longitude ,(5 degrees 48 minutes West),could have been set wrongly in the computer . In comparing the four chosen waypoints as entered , there is a strong suggestion that the first two were not derived from the same source , or by the same method , or by the same person as the last two.....due to the number of decimal places used ....

If the longitude value were intended to be "5 degrees 49 minutes West" , the waypoint would have been safely out at sea , and would have guided them to pass to the west (offshore) of a lighthouse on the coast , a prominent landmark when visible in good weather.......
........some persons will write a numeric 9 with curling bottom leg , which can sometimes be confused with a numeric 8 , this simple change would be enough to move the waypoint inland ..(one minute of longitude at this point on the earth's surface is slightly over 1000 metres)....
Similarly , when the numbers were being entered manually using the keypad on the computer itself , it would be easy to inadvertently press the 8 key instead of the 9 key , as they are side by side on the keypad........
Another possibility is that the waypoint location was chosen when looking at an Ordnance Survey based map of the area . Such a 1:25,000 or 1:50,000 scale OS map , or the 1/4 mil aviation map (which was based apon an OS map but with aviation information overprinted ) all of which at that time had/still has a grid printed apon it which may at first appear to be aligned with north , but is in fact somewhere in between true and magnetic north . ( all OS maps have this grid , but the alignment can vary depending on the exact longitude area which they cover....)
If a suitable waypoint offshore were chosen , and the longitude co-ordinate taken from the scale at the bottom edge of the map , by wrongly using a ruler aligned with the grid as described , what seems to be a safe waypoint well away from the cliffs and mountains may be selected on the map , but in reality it is a point which is some distance inland as mentioned above.....(.This variation of OS maps is not known and understood by everyone.....for a more detailed explanation of this odd effect go to "gneiss.dyndns.info/chinook5.htm" )
This possibility gains credence when the second waypoint is studied . This is at a point where the Great Glen narrows down , and is named the Corran Narrows . Again it is only listed to an accuracy of whole minutes of latitude and longitude , (whereas the last two waypoints were listed down to decimal fractions of minutes) , and again it appears to be offtrack to the East....
In this case the obvious place for a waypoint is the lighthouse in the middle of the valley , but the co-ordinates are for a point on the south-eastern shore , which would have to be overflown at at least 700 feet agl. to be safe , as a hill 'Druim na Birlinn' at 206 metres height , is almost directly in line with the waypoint..
A fourth possibility is that obtaining fractions of a minute of longitude was not possible from the map used in planning the flight , and so the nearest whole minute was used , ie. rounding up or down . Rounding up to the nearest whole minute in this case would give 5 degrees 49 minutes longitude as described above , providing a waypoint that is offshore abeam the lighthouse . Rounding down gives 5 degrees 48 minutes which is the co-ordinate used for the fatal flight . In other parts of the world in which the RAF has operated or is still operating today , such as Bosnia and the Gulf , the longitude is East of Greenwich and so rounding down a longitude here would move the intended waypoint to the West...thus it could happen that the co-ordinate was rounded down by habit intending to move it to the West.......but inadvertently moving it to the East......inshore and up on the mountainside....(rounding up or down of latitude has a smaller effect in this case) Again looking at the location of the second waypoint in the route , at Corran , if the longitude is rounded up to 5 degrees 15 minutes , it brings us to about the middle of the valley with the Corran lighthouse just a little on the right as we approach.....far more logical and much safer..... The higher accuracy used for the last two waypoints on the route suggests they came from a reference source or other documentation

Thus the point towards which they were flying was further East than they probably realised , and above the height at which they would normally fly across the sea . To make things even worse , they were using GPS satellites as their navigation source , and we know from later analysis that there was a considerable error on the signals , effectively moving the selected waypoint further inland and further up the mountainside...If they were looking for a recognizable point , which is normal flying practice , they may have seen a cottage up on the mountainside just visible in the mist , and mistaken this building for the lighthouse complex . They certainly passed very close to overhead this cottage in the final seconds before the major impact , and it is the only other building for miles around .
There have been suggestions that they spotted the 'lower' foghorn station and mistook this for the lighthouse , but this almost laughable , as the 'lower' foghorn is only the size of a single car garage , white walls and a flat dark grey roof with railings............and this was off to their right-hand-side as they passed it some seconds earlier . Had they mistaken this for the lighthouse they could be expected to commence a gentle left turn onto a northerly heading at that time , whereas their course was maintained in a straight line....
This cottage though is ten times bigger , and far more similar in size to the lighthouse complex and thus far more likely to be mistaken for it.....the testimony of the lighthouse keeper who was driving down the hillside mentions that the crash appeared to happen just behind him......implying that he was driving down the straight part of the road toward the cottage and towards the approaching aircraft , thus it is possible that seeing the headlights of the landrover in rough alignment with the cottage gave the illusion of a lighthouse being directly ahead..... So.....encountering terrain much higher than anticipated , and which was masked by the mist , may have been the final factor in causing the crash....Judging the relative height of an object which is being approached is harder in a helicopter due to the variations in attitude in different flight modes.....ie. the aircraft can tilt forwards when accelerating and the horizon effectively moves up the windscreen....
GPS data recovered from the navigation computer indicates that the helicopter continued in a straight line right up until the impact which does suggest that the crew were confidently continueing their planned route , or were distracted , and saw no indications of their proximity to rising ground until it was too late...
One possible distraction was the compass indication...........there are published values to apply to compass bearings in order to obtain the corresponding true values . This 'variation' was 7.5 degrees in Northern Ireland and this was the value which they applied to their initial route leaving Northern Ireland . This 'variation' is an average value expected to work over a large region and increases slowly as one travel East across the UK for example......but the variation measured at the crash site revealed a value of 12.5 degrees , this would have been sensed automatically by the compass equipment in the aircraft and applied to instruments on the pilots panel . ( This is not unusual for Scotland due to the large amount of igneous rock and there are documented cases of high local variations being observed ie.Skye , Blairgowrie...)........this could also explain the navigation anomaly experienced by the yachtsman..(.the last witness known to have seen the aircraft in flight)...he thought he was 2 nautical miles south west of the lighthouse at the time , but that point is a long way from the track of the aircraft , it would have passed over a mile away from him.....but if he was navigating by magnetic compass and was experiencing the same magnetic variation of 12.5 degrees this would place him much closer to the best guess track of the chinook ......ie. SW is 225 degrees true , seeing this on the compass card whilst experiencing a local magnetic variation of 12.5 degrees gives a true angle of 212.5 degrees from the lighthouse , placing him further south and East ...
Thus as the flight progressed using an initial track of 28 degrees magnetic , it would have diverged from the direct route to waypoint A as shown by the navigation computer . Increasingly the computer would be saying that they had to turn right until a crosscheck would show that a track of 35 degrees magnetic was required to reach the waypoint . In addition of course they had to steer into wind as well , another 8 degrees to add to make up their actual heading .......Changing the navigation computer source over to the Doppler data would show that the two (Doppler and GPS) had diverged also , and that difference was increasing as the flight progressed.........not unusual and a known failing of Doppler systems . From the indications stored and recovered later we know that the Doppler was saying that a slight left turn was needed.......at the point where they were getting close to waypoint A and they changed over to waypoint B , the Doppler was saying that a left turn of 10 degrees was required . The last thing you need when the visibility is reducing is to find that all the navigation equipment is disagreeing......
The maps and routing details did not survive the crash , but a photocopy of a map was left at Aldergrove which shows a route passing close to the lighthouse . It is entirely possible though , that they chose a slightly different route after checking the weather expected around the Kintyre peninsula.......so for a complete picture it is best to examine any other possible intended locations for waypoint A.....
There are at least two significant locations further along the coast of the Mull to the east , which fall on the same latitude as entered into the navigation computer for waypoint A ,(assumed by most to be intended as the lighthouse) , and in both cases their longitude differs only by one number from that of the stored value of waypoint 'A'.....this possibility is described below at length..........

THE ALTERNATE ROUTE SCENARIO

Flying a helicopter without proper floats , a complex mechanical device at the best of times , the last thing a crew would want is to fly long distances over water with so many persons on board . The chances of everyone exiting the a/c successfully in the event of a problem leading to ditching would be low . ( A Chinook will reputedly float for 30 minutes if it lands gently in one piece , upright , on a calm sea , but in the 1986 Shetland Chinook crash 45 lives were lost) It is not known if any of the passengers had undertaken ditching survival training in a tank , normal practice for north sea oil rig workers ...it seems unlikely as they were not expected to be regular travellers (in this way)....The obvious solution when tasked with this problem , is to cross open water as quickly as possible , and plan a route never too far from land.......which allows you lots of places to stop ....For example if an error indicator light should become illuminated , often the recommendation is to land at once , check the oil level or whatever and check with engineering if possible before proceeding.......

On the morning of the planned trip , the latest weather forecast was not too good , with low cloud , mist and fog in places . This meant it would be a more difficult journey , but still possible....
The aircraft which they had to use was one of the first , newly converted , MK2 Chinook's , which had numerous teething problems ie...

Lots of the 'reference cards' which the crew had to refer to for information and guidance before and during a flight , were incomplete ...
The conversions were plagued with poor electrical connections and intermittant flashing error lights ...
Some electronic equipment appeared to suffer from electrical interference.......
They were not allowed to climb anywhere near to an altitude where icing might occur ......
They were not allowed to fly under Instrument Flight Rules (IFR) , as the a/c was not fitted with approved equipment for this mode of flight..
This meant that they had to remain in sight of the ground or sea at all times if possible....... ..or face disciplinary action.......

Once the crew realised that they had to use a MK2 Chinook they may have revised the planned flight . It would be prudent to have chosen a route via flat safe landing points in case they were needed . The golf course area in the south end of the Mull of Kintyre provided such a large flat area with fields , making it an obvious point to aim for if crossing the sea . There is also a link to a smaller beach and pasture area just around the headland to the West known as Carskey Bay . Their route could have continued via Machrihanish airfield and then onward further to the north , where there are more flat areas of pasture along the West coast of the Mull , and good wide beaches too .....

So maybe they planned to fly from Ireland across towards the Mull of Kintyre and cross the Scottish coast over the golf course at Dunaverty , near the community of Southend .....from here there is a wide valley heading roughly north over this part of the Mull , the high point of the valley is only 81 metres above sea level (asl) which would allow them to avoid the highest ground where the worst weather was forecast .......The main road to Southend , the B842 , follows this route , known locally as Conie Glen ........

This is a view of the main bulk of the Mull from Dunaverty golf course , the faint outline of the Irish coast is just visible in the distance...

This is a view looking inland from the golf course , the start of the valley is visible far right ..

This is the relevant part of an aviation map of that time , the black line departing from Aldergrove (bottom left)is the direct track to the golf course on 035 degrees magnetic....the red line is the track which the aircraft appears to have taken , closer to 027 degrees magnetic , and leading to the obscured high ground....... ..

The crew had a great deal of experience at low flying.....it was an everyday event for them.....and they would have been able to fly up the valley at 500' and reach RAF Machrihanish via this route.........miss all the really bad weather ....and continue the remainder of the journey from there. Machrihanish was still an active airfield with a radio navigation beacon which they could tune in to , and as mentioned could be a good emergency stopping place if needed.
The latter part of the journey further to the north and east was expected to be under better weather conditions ........

This is an OS map of the area of Dunaverty golf course ,(bottom just right of centre), showing the valley northwards , heights shown are in metres amsl,( 100 metres is 328 feet ),the OS grid is not aligned exactly to true north . Carskey Bay is far left .

The similarity of the co-ordinates is illustrated below ,and we should consider the chances that during planning , programming , or maybe later during the flight , one number had become transposed . The values found to have been entered into the navigation computer for the first waypoint were NOT those of a place on the coast near the golf course , or of Carskey Bay , but those of a rocky hillside , some miles away . This point was inland , at an elevation above that which they were thought to have been crossing the sea , and a slightly shorter journey to reach . The nearest landmark was a lighthouse ... sometimes used as a waypoint in good weather and at a very similar Latitude and Longitude to both Dunaverty golf course and the beach in Carskey Bay.....eg...

lighthouse..........55 18.5 N 05 48 W

golf course.........55 18.5 N 05 38 W

Carskey Bay.........55 18.5 N 05 41 W

This may have been a machine error or a human error , early keypads were notorious for 'rollover' error , where the logic circuitry decoding what were actually simple switches , could sometimes behave strangely . Often if two keys were inadvertently pressed together , the logic might only 'see' the last one pressed or the last one released . Obviously there are checks on modern computer keyboards to sound an error beep when unprogrammed combinations of keys are pressed .
Bounce was another problem , as the contacts in most switches actually do not make perfect contact instantly , but bounce for a very short time , and can give the indication of multiple keystrokes unless the logic includes an element of'de-bouncing' to damp the signal...usually a short time delay of a few milliseconds during which time any further keystrokes are ignored.
Interference.....any impulse noise , electrical interference from other equipment , power busses being switched in or out etc. could cause the keypad decode logic to wrongly interpret the keystrokes especially if they happened at the moment a key was pressed .....this is more likely to be a problem where the installation has not been tested to eliminate such possibilities , as was the case with this aircraft....

Corruption of the stored data after the flight departed SHOULD be detected by error checking logic , giving a "CHECKSUM" error.....but under some unusual conditions , the data could get changed without any error warning to the crew . Imagine then , a radio call for example , may have corrupted the data via EMI (Electro-Magnetic Interference.....unintentional signal coupling emitted from other equipment). All that is visible to the crew is that the heading bar jumps , then settles down on a new deflection . Switching from GPS to the Doppler source and back again shows fairly close agreement between the two sources....you check that you still have the same waypoint selected....all looks ok......so you continue , unaware that you are now being guided to a different location...........

Human Factors...although some people aquire 'touch typing' skills on typewriters or computers , most persons using a keypad will look at the keys when actually pressing them , type in a whole number or sequence , then look at the screen/display to check that the correct information has been accepted......
It is sometimes easy to mis-interpret numbers if written by someone else , especially if there are corrections , alterations or changes.....
A check on the predicted heading and distance from waypoint 'A' to waypoint 'B' would still show the expected figures due to the distance involved...ie. a crosscheck of the route would look good .

However it happened , the effect of this fault or mistake would have been to guide the a/c to the west of their intended course and towards to lighthouse....instead of the golf course (035 degrees magnetic track from Aldergrove)....or the beach in Carskey Bay (035 degrees magnetic track from Carnlough on the Irish coast)
This would not have been apparent over the first half of the journey to the Mull , as they were navigating in and around the Antrim hills on their way to the Irish coast.........once out over open sea , the difference between the track they expected to fly , 035 degrees magnetic , and that which the navigation computer equipment was indicating they should fly , would have become apparent , and as they got nearer to the Mull , have become increasingly obvious ...........with all four crew taking some interest in navigation , I think it is fair to assume that the difference would have been noticed and discussed ..

This difference oddly , was about 8 degrees , the same as the magnetic variation in Ireland at the time .

During flight planning it is common to have to switch and convert between magnetic and true bearings ....as some equipment can only use magnetic headings, ie.compass.....many maps are drawn with a grid superimposed which is aligned to true north , and some can use both ie. GPS navigation boxes ....

With no visual reference point , as they were in mid channel and out of range of other radio beacons , they would have had to decide what to believe , whether it was an error measuring angles or applying the magnetic variation during planning , or whether the wind had changed round to the S/W . The low lying area of coast around the golf course was over a mile wide , presenting a relatively large target , and so small errors would not matter too much . A change in the forecast wind direction could explain how they seemed to be too far East.....whatever the reasoning they could have elected to use the navigation computer equipment heading .... ..This computer used inputs from two sources , a Doppler radar source and a GPS satellite receiver source . It is thought that a comparison between the two sources whilst half way across the open sea would have shown them still to be in fairly close agreement...ie maybe two degrees difference.

Although they could see the misty outline of the Irish coast behind them , and see the sea surface below them , there was a bank of fog ahead covering the whole area of the Mull of Kintyre , a well known rocky headland . This was due to the southerly moist wind being forced up over high ground , an effect familiar to the local population . Known as orographic cloud or fog it usually has a clearly defined base , and a uniform texture . It also persists over the top of the high ground and starts to break up where the air descends on the lee side of the hill . On this day the base of the cloud was at the height of the lighthouse , and as it extended some distance out to sea from the coast , it blocked visibility of the lighthouse from an aircraft flying above this level . The actual coastline would also be concealed as the aircraft came closer......(It did allow sight of the coast from sea level however).... There were also other , higher layers of cloud with some gaps allowing occasional patches of sunshine .

There is a phenomenon familiar to most pilots , whereby the visibility straight down can be quite good , but if the local weather is layers of mist , cloud , fog , dust or smoke haze , then visibility ahead is restricted , where the pilot is looking down diagonally through the layers . This can be exacerbated by sunlight and/or the direction from which the light is coming . In this case the sun was behind them to the left(about 270 degrees) , and out at sea the visibility 7 to 10 miles in haze horizontally .
So it is quite possible that they navigated towards the Mull in what might have been considered a 'greyout' situation , even on a day with good weather generally , the colour of the sea and some cloud present can offer this condition , where it is almost impossible to determine the horizon or the point where sky and land/sea merge , your eyes have nothing to focus apon and you spend more time consulting the instruments inside the aircraft..

.....Trusting the navigation computer they could not have been aware how close they were to the lighthouse and the high ground , all obscured in the local fog......(the meteorological definition of fog.. is mist or low cloud where the visibility is less than 1000 metres)
As they approached this first waypoint , the normal 'alert' indicated to them that they were one minute flying time from this point , they responded by selecting the next waypoint along their route , waypoint 'B' near Corran , and continued on the same heading . They could not fly directly to this second waypoint as it would involve flying over other high mountains and the best route available to them in this scenario was up the valley to Machrihanish , then following the coastline north . There was no dangerously high ground within miles of the golf course and that they could follow a valley easily once they got some visual clues . It is thought they commenced a gentle climb which would also have reduced their speed slightly . It would have suited them to overfly the waypoint 'A' , but it was not critical , and in fact they were slightly off course to the right .They could relax a little once they were over land again.....

This is the most likely track of the a/c over the last few seconds of flight .
There is a 95% probability that they first touched the ground near to the point marked as '500 feet rocks'

The fog may have seemed thicker than they expected .......quite reasonably low ground like the golf course could be expected to be almost clear as it was only a few feet above sea level . Maybe some residual mist/fog from Sanda Island which the prevailing wind would blow in that directon......

Then .....when they thought they still had over 20 seconds to run to pass over the beach........they should have found that they were crossing a shoreline at an oblique angle , with rocky terrain approaching the height at which they were flying . They should have had an automatic altitude alert almost immediately . Quite violent control actions would have been needed to avoid contact only seconds after becoming visual with the ground surface.......it is highly likely that they did scrape the ground . As the flight controls are hydraulic assisted......any damage done at this time could have made the aircraft harder to manoeuvre.........if a rotor tip made contact with anything , heavy vibration would follow........ .......both pilots acting together may have barely been able to impose any control action.......... as in the Chinook helicopter , differential collective movement of the blades on the two rotors are required to alter the flight angle and proceed to a climb.... .......whereas in normal aircraft only the elevator on the tail has to move......in addition there was no power lever for the engines , they were under electronic control to respond to demands automatically..
With the restricted visibility the obvious reaction is to climb straight ahead.........in fact they had high ground only on the R/H side (starboard) , and ground sloping down to the sea on their left (port)..

Then there was a second major impact................

The accident investigation found the main crash site , and the debris was scattered over a wide area , but as they did not know at the time , the exact heading which the a/c had approached from , had no reason to suspect that there may have been an earlier impact which possibly disabled the a/c ..........
Most of the control parts were found and identified , but it was impossible to determine what damage had occurred at the time of the main impact , as distinct from any which had occurred at an earlier time .
The flight conditions were very poor at and around the crash site , and there was conjecture for many years about the true cause of the accident , as there was very little recorded information about the last few moments of this flight( Unlike the recorders or 'black boxes' fitted to airliners ...which can record the voice conversations of the crew , and the movement of important control levers/surfaces , giving a more informative picture of events in some detail )....

That information which was available has been examined in great detail , but mostly with little result , as it gives no real clue to the cause of the crash , and it has all been covered in other documents . The only relevant facts here are that the handling pilot had the heading of 035 degrees set on his panel ......the navigation radio was set to the frequency of the beacon at Machrihanish ...and the navigation computer was set to use the GPS source ...
The navigation radio would not have been useable as the beacon was on the opposite side of the mountain , the signal being blanked.....if they had proceeded up the valley from the golf course , the signal would have been available to them at about the halfway point ......
It was found in further analysis that the GPS data and the Doppler source data had diverged.....this was not unusual , but in this case the difference was significant inasmuch that the GPS source which they had chosen to use had guided them more towards the higher ground , whereas the Doppler source would have led them dangerously close but more towards the coastline..

With no obvious cause at the time , this led to some diverse opinions , as not all involved in the investigation could agree apon a cause or verdict ............some became quite 'blinkered' by their own pet theory....the fact that the helicopter had flown only a little over 50 hours since it was virtually re-built in the factory led many to suspect a mechanical problem..
Unfortunately the persons in the highest authority had the most extreme view...... which they imposed apon everyone else ......accusing the crew of recklessly flying at high speed toward the highest part of the Mull , without explaining how they were so sure that the crew knew where the high ground was..????...

This did appear to be politically and financially expedient for the government at the time , and also directed embarassing questions away from other core issues....such as whether the helicopter was really 'fit for purpose' at the time of the flight..... Successive governments have continually failed to disclose all the true facts , and shied away from the shake up needed inside the MOD....allowing many of the failings to be perpetuated , and all of those employed in the MOD at the time to continue in employment or enjoy pensions..............